This invention relates to an improved process for dewaxing vegetable oils and, more particularly, to a process in which consistently efficient separation of undesirable waxes can be achieved for oils such as sunflower, safflower, and corn oil. Vegetable oils, and more particularly edible vegetable oils, are used as salad oils, cooking oils, margarine constituents, and the like. Safflower, sunflower and corn oil in particular are oten used in these and other food applications.
For purposes of this application the terms "wax" and "high melting material" are used interchangeably and are intended to be generic to the many substances which can cause clouding in oils at temperatures of less than about 60.degree. F.
A problem which arises in the purification of vegetable oils is that the crude oils tend to have high contents of undesirable unsoluble material. Natural vegetable seed oils are composed of mixtures of many naturally produced chemical compounds including not only the oily constituents, but also usually, small percentages of natural phosphatides, vegetable waxes, pigments, and many other compounds. The oily constituents, namely the glyceride esters of the long chain fatty acid of the saturated and unsaturated types make up the largest fraction of vegetable oils. Such materials to a large extent determine the properties of the oil, but the remaining constituents also exert a marked and sometimes detrimental effect, depending upon the use to which the oil is put.
Some natural vegetable oils of commercial grade such as safflower, sunflower, cottonseed oil, soybean oil, peanut oil and corn oil become cloudy after having been chilled or cooled to somewhat lower than room temperatures as in a refrigerator and remain cloudy when returned to ordinary (room) temperatures. The cloudiness may be followed by a settling out of an opaque layer, a particularly disadvantageous occurrence when the oil is packed in glass and where clarity and brightness are of importance.
A large portion of the high melting material can be removed from oils by a process known as "winterizing" in which the oils are carefully cooled to low temperatures for extended periods of time to permit precipitation of solid material. Solid material can then be removed by pressing or other separation procedures. However, not all of the high melting solid material is removed from oils by winterizing, and the oil still tends to cloud when stored for extended periods of time at low temperature. Moreover, the usual winterizing treatment undesirably tends to remove by entrainment a substantial portion of the olein fraction of the oil.
The process of this invention presents a process for producing a salad oil which remains clear at ambient to refrigerator temperatures. This process is useful for processing oils which contain waxes such as sunflower, safflower, or corn oil. A number of oils such as those mentioned above contain small quantities of waxes which are derived from the seed coats during crude oil extraction. These waxes precipitate at room temperatures or lower, making the oils unsuitable for use in salad oils. In the past these waxes have been partially removed by expensive processes involving low temperature crystallization and filtration at very slow rates.
The dewaxing process of this invention is useful primarily for oils which have been previously refined and either water-washed or filtered. It is important that the oils have a low fatty acid content of less than about 0.1% and in addition the oils should have a low soap content of less than about 0.1%. The use of normal crude oils in the process of this invention is practically impossible because of the many impurities present.
Many previous attempts have been made to remove wax fractions from crude vegetable oils by mechanical separation such as centrifuging and filtration at low temperatures. These techniques have been unsuccessful due in part to the small differences in specific gravity between the wax and the vegetable oil and also due to the compaction of the vegetable oil wax under pressure in a filter to a slime or grease consistency which resists the passage therethrough of the vegetable oil.
Refining techniques previously in general use, such as alkali treatment of oil, will not remove wax from vegetable oils sufficiently to eliminate the cloudy appearance of the oils due to the presence of wax, particularly at lower temperatures. Treatment of vegetable oils with bleaching earth reported as an effective method of removing mucilaginous materials is not effective at low temperatures, as the slimy nature of the vegetable oil wax prevents satisfactory removal of the treatment material. Another common approach to refining of oils is the hydration of gumming material, making them insoluble. However, addition of water to vegetable oil per se does not render the wax any more oil insoluble or more readily recoverably by any mechanical methods.
In view of the above, it is an object of this invention to provide an improved process for the dewaxing of refined and water-washed or filtered vegetable oils.
It is a further object of this invention to provide a dewaxed vegetable oil which is suitable for use as a salad oil after it has been bleached and deodorized.
It is an additional object of this invention to provide a dewaxed vegetable oil having excellent refrigerator clarity of greater than 100 hours at 32.degree. F and greater than 2 weeks at 40.degree. F.
These and other objects will become apparent from the discussion below.